Lines homozygous for single structural genes (isocistron lines) of ODH will be established and analyzed for cryptic variation within the ODH locus. Lethals linked to ODH will be identified and mapped relative to it and to inversions, establishing chromosome segments that can be assessed for their balance relative to each other. In this way, the amount of cryptic variation at one locus can be ascertained for a wild species having small, linear populations. The relation of ODH variants, cryptic and otherwise, to specific lethals may discover the extent to which this limited portion of a gene pool is structured, both by positive (active ODH alleles) and negative (lethal) factors, and can lay the foundation for analyzing the history of cryptic variation and of specific lethals and balanced lethal systems in the long term evolution of the virilis group. Investigation of methods for placing adult Drosophila into cold storage will be completed through study of means to compensate for excessive dehydration of stored flies, of interstrain differences in longevity, of interstrain hybrid responses to cold, and of effects alternating temperatures as a pretreatment for cold storage.